/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import static java.util.Objects.requireNonNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.collect.Maps;

import java.util.Map;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * This class provides a skeletal implementation of {@link ValueGraph}. It is recommended to extend
 * this class rather than implement {@link ValueGraph} directly.
 *
 * <p>The methods implemented in this class should not be overridden unless the subclass admits a
 * more efficient implementation.
 *
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 * @author James Sexton
 * @since 20.0
 */
@Beta
@ElementTypesAreNonnullByDefault
public abstract class AbstractValueGraph<N, V> extends AbstractBaseGraph<N>
        implements ValueGraph<N, V>
{

    @Override
    public Graph<N> asGraph()
    {
        return new AbstractGraph<N>()
        {
            @Override
            public Set<N> nodes()
            {
                return AbstractValueGraph.this.nodes();
            }

            @Override
            public Set<EndpointPair<N>> edges()
            {
                return AbstractValueGraph.this.edges();
            }

            @Override
            public boolean isDirected()
            {
                return AbstractValueGraph.this.isDirected();
            }

            @Override
            public boolean allowsSelfLoops()
            {
                return AbstractValueGraph.this.allowsSelfLoops();
            }

            @Override
            public ElementOrder<N> nodeOrder()
            {
                return AbstractValueGraph.this.nodeOrder();
            }

            @Override
            public ElementOrder<N> incidentEdgeOrder()
            {
                return AbstractValueGraph.this.incidentEdgeOrder();
            }

            @Override
            public Set<N> adjacentNodes(N node)
            {
                return AbstractValueGraph.this.adjacentNodes(node);
            }

            @Override
            public Set<N> predecessors(N node)
            {
                return AbstractValueGraph.this.predecessors(node);
            }

            @Override
            public Set<N> successors(N node)
            {
                return AbstractValueGraph.this.successors(node);
            }

            @Override
            public int degree(N node)
            {
                return AbstractValueGraph.this.degree(node);
            }

            @Override
            public int inDegree(N node)
            {
                return AbstractValueGraph.this.inDegree(node);
            }

            @Override
            public int outDegree(N node)
            {
                return AbstractValueGraph.this.outDegree(node);
            }
        };
    }

    @Override
    public final boolean equals(@CheckForNull Object obj)
    {
        if (obj == this)
        {
            return true;
        }
        if (!(obj instanceof ValueGraph))
        {
            return false;
        }
        ValueGraph<?, ?> other = (ValueGraph<?, ?>) obj;

        return isDirected() == other.isDirected()
                && nodes().equals(other.nodes())
                && edgeValueMap(this).equals(edgeValueMap(other));
    }

    @Override
    public final int hashCode()
    {
        return edgeValueMap(this).hashCode();
    }

    /**
     * Returns a string representation of this graph.
     */
    @Override
    public String toString()
    {
        return "isDirected: "
                + isDirected()
                + ", allowsSelfLoops: "
                + allowsSelfLoops()
                + ", nodes: "
                + nodes()
                + ", edges: "
                + edgeValueMap(this);
    }

    private static <N, V> Map<EndpointPair<N>, V> edgeValueMap(final ValueGraph<N, V> graph)
    {
        Function<EndpointPair<N>, V> edgeToValueFn =
                new Function<EndpointPair<N>, V>()
                {
                    @Override
                    public V apply(EndpointPair<N> edge)
                    {
                        // requireNonNull is safe because the endpoint pair comes from the graph.
                        return requireNonNull(graph.edgeValueOrDefault(edge.nodeU(), edge.nodeV(), null));
                    }
                };
        return Maps.asMap(graph.edges(), edgeToValueFn);
    }
}
